Re: [PATCH] net: dsa: mt7530: increase reset hold time

[Arınç ÜNAL]

On 13.03.2024 16:13, Justin Swartz wrote:
> On 2024-03-13 14:06, Arınç ÜNAL wrote:
> > On 13.03.2024 14:52, Justin Swartz wrote:
> > > On 2024-03-13 10:59, Arınç ÜNAL wrote:
> > > > This ship has sailed anyway. Now the changes the first patch did must be
> > > > reverted too. I will deal with this from now on, you can stop sending
> > > > patches regarding this.
> > >
> > > At least if the first patch isn't reverted, the approach used is
> > > less likely to result in the problem occuring, IMHO.
> >
> > I disagree that the previous approach is less likely to result in the
> > problem occurring. If you don't like the delay amount we agreed on, feel
> > free to express a higher amount.
>
> I created and tested a patch to entertain your input about what you
> thought could be a suitable hold period to address the problem, and it
> appeared to work. The criteria being that the crystal frequency selection
> was correct over 20 tests.
>
> So if only the reset hold period is going to change, I'm good with what
> you had suggested: 5000 - 5100 usec.
>
> Ultimately the selection of this period should be guided by the timing
> information provided in a datasheet or design guide from the manufacturer.

That's a good point, I agree.

> If you, or anyone else, has such a document that provides this information
> and is able to confirm or deny speculation about any/all timing periods
> related to reset, please do so.

These are the documents I use to program this switch family. I did not
stumble upon a page going over this.

MT7621 Giga Switch Programming Guide v0.3:

https://github.com/vschagen/documents/blob/main/MT7621_ProgrammingGuide_GSW_v0_3.pdf

MT7531 switch chip datasheet:

https://wiki.banana-pi.org/Banana_Pi_BPI-R64#Documents

> > I also disagree on introducing a solution that is in addition to another
> > solution, both of which fix the same problem.
>
> I'm not sure I understand why you say that. These patches were intended
> to be applied exclusively, or in other words: in isolation - not together.
>
> Although if they were applied together, it wouldn't really matter.
>
> For the record, I've only continued to keep this thread alive in the
> hope that some solution to this problem will make it into mainline
> eventually.
>
> I don't care if it was my original patch, the subsequent patch, or a
> later patch provided by you or someone else. :)

I think you've missed that your patch is already applied. And it won't be
reverted for reasons explained by Paolo in this mail thread.

https://git.kernel.org/netdev/net-next/c/2920dd92b980

So if your patch here were to be applied too, the final mt7530.c would have
the LEDs disabled AND before reset deassertion delay increased.

Arınç